(a) Field of the Invention
The present invention relates to a thermal shutdown unit, a switch controller including the same, and a method controlling a thermal shutdown protection operation. Particularly, the present invention relates to a thermal shutdown unit, a switch controller including the same, and a method controlling a thermal shutdown protection operation to prevent damage due to a heat generated in a switch controller and a power switch applied to a switch mode power supply device.
(b) Description of the Related Art
A switch mode power supply device (hereafter, SMPS) rectifies an input AC voltage into an input DC voltage (referred to as a dc-link voltage), and converts the input DC voltage into a DC output voltage of another level. In this case, the output DC voltage is higher or lower than the input DC voltage. The SMPS is generally used for electronic devices such as a battery charger of a mobile phone and an adaptor of a laptop computer.
In general, the SMPS controls a switching operation of the power switch of the primary side according to the magnitude of the current supplied to the load to control the current amount flowing in the power switch of the primary side. The SMPS feeds back the output voltage to the capacitor of the primary side, and controls the duty of the power switch of the primary side through the feedback voltage charged to the capacitor of the primary side to constantly maintain the output voltage.
In detail, the SMPS decreases the feedback voltage charged to the capacitor when the current amount is decreased such that the output voltage is increased, and decreases the feedback voltage charged to the capacitor when the current amount is increased such that the output voltage is decreased.
When the load connected to the SMPS is an overload, the heat generated in the SMPS is increased, and if the SMPS is continuously operated in a high temperature environment, an operation error or damage due to the heat generated in the SMPS is generated in the controller controlling the operation of the SMPS. To prevent this, a thermal shutdown (TSD) block having a TSD function to shut down the operation of the SMPS according to the heat generated in the SMPS is applied to the controller.
In detail, to sense the heat generated in the controller, a power switch including a thermal sensing circuit may be mounted, however this power switch increases the production cost of the SMPS.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.